1. Field of the Invention
This invention relates to a diffusion transfer photographic process, and more particularly to an improved photosensitive silver halide to be used as a photosensitive material in the method of forming black and white negative silver images according to the diffusion transfer photographic process as described in U.S. Pat. No. 3,615,438. Hereinafter this method is referred to as the solubilization by incipient development method (hereinafter defined as SID method).
2. Description of the Prior Art
The SID method is a method of forming black and white negative transfer images according to the diffusion transfer photographic process. More particularly, this method utilizes a phenomenon whereby the dissolution in unexposed areas of silver halide particles by a solvent for silver halide is inhibited, and the dissolution in exposed areas of silver halide particles is promoted (that is, promotion of development solubilization), so that silver halide in exposed areas is selectively dissolved in a developer and silver ions are precipitated on an image-receiving layer.
This invention is directed to an improvement in halide composition photosensitive silver halide for use in the SID method.
For providing negative transfer silver images by the SID method, U.S. Pat. No. 3,615,438 discloses a method in which the solvent for silver halide (for example, sodium thiosulfate) and a development solubilization promoter (for example, 1-phenyl-5-mercaptotetrazole) are quantitatively balanced.
According to this method, however, it is difficult in practice to obtain negative transfer silver images for all types of silver halide emulsions, e.g., having different halide compositions. For example, AgBr, AgCl and AgBrCl emulsions are liable to provide positive transfer silver images. Even if negative transfer images are obtained, it is necessary to use a large amount of a development solubilization promoter in order to keep the maximum density (D.sub.min) at sufficiently low levels. This gives rise to several problems, in that the development requires an unusually long period of time, and the sensitivity and maximum density (D.sub.max) decrease.